Repetitive, secure access to a blood vessel is often required by patients with chronic diseases. A subset of these patients, dialysis patients, require access to a high flow vessel.
For example, end stage renal failure patients need repeated, chronic access to the vascular system to allow life sustaining hemodialysis. In the United States, an estimated 421,349 patients per year undergo hemodialysis and, thus, require maintenance of a vascular access site. The annual estimated cost associated for dialysis patients is approximately $73,000 dollars and a significant portion of these costs is spent on maintaining vascular access capability. Cumulatively, $30.9 billion U.S. dollars/year are spent, equal to approximately 7.1 percent of the Center for Medicaid and Medicare Services total budget (United States Renal Data System 2015 USRDS annual data report: Epidemiology of Kidney Disease in the United States. National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Md., 2015).
Repetitive puncture of a blood vessel in a localized area may ultimately lead to weakening of the vessel wall in that area that can result in aneurysm formation (a ballooning out of the vessel wall) which may eventually rupture with serious bleeding. A blood clot may also form within the aneurysm that can ultimately cause a thrombosis (blood clot) of the fistula.
Furthermore, repetitive needle punctures of a blood vessel may result in damage to the vessel wall causing scar tissue formation, narrowing the vessel (stenosis), and causing it to be nonfunctional.
Another complication of repetitive punctures is hematoma formation. This may be caused by back wall vessel perforation by a needle after penetrating the front wall, or upon needle extraction from the front wall, if inadequate pressure is applied to the blood vessel to allow sealing of the puncture hole with a blood clot.
Still further complications may occur if, after extraction of the needle from the blood vessel, excessive pressure is applied to the vessel to avoid leakage from the puncture hole. The excessive pressure may shut off blood flow in the vessel, resulting in a complete clotting of the vessel.
Currently, there are three commonly used systems to establish vascular access for kidney failure patients: catheter-based access, native arterial venous fistula, and synthetic graft fistula. All techniques commonly have complications that require interventions to reestablish access.
Catheter-based access. This system may include a synthetic catheter that is placed transcutaneously, allowing the dialysis technician to attach the patient's catheter to the hemodialysis machine. Although this system offers immediate availability for use after placement, there may be several disadvantages. First, the system may be prone to infection, particularly for transcutaneously placed catheters where infection can develop at the skin exit site due to inadvertent breaks in the sterile technique by technicians. The presence of a foreign body in the vascular system is prone to seeding from distant sources of infection in the patient via the bloodstream. When a catheter becomes infected, removal is usually required to clear the infection. As a result, another catheter must be placed at another site to resume treatment. This requirement results in the additional cost and inconvenience of performing an additional surgical procedure as well as the cost of the replacement catheter.
Second, the relatively small caliber of the synthetic tubes placed in the vascular system may permit only limited blood flow through the system while a patient is on the dialysis machine. This may prolong the time each patient needs to be dialyzed and may indirectly contribute to the frequency of dialysis treatments.
Third, the catheter system introduces a foreign body in a central vein. This can lead to further complications including, for example, frequent formation of fibrin clots or blood clots in the lumen of the tube requiring the infusion of costly thrombolytic drugs to clear the catheter. Sometimes even more costly endovascular procedures are required to reestablish function in a catheter. Furthermore, the foreign body in the vascular system may result in a thrombosis or a narrowing (stenosis) of a major vein (subclavian vein or superior vena cava) that then precludes using that vein for future venous access in that patient. This complication can have life threatening ramifications particularly if the stenosis involves the superior vena cava.
Native Arterial Venous Fistula. A second mode of vascular access requires the construction of a connection between a patient's native vein and an adjacent artery (an Arterial Venous (AV) fistula), that creates a high flow of blood through a limited portion (generally 15-20 cm) of the patient's vascular system. This superficially positioned native vascular conduit usually grows to a certain minimal size (approximately 5-6 mm or greater in diameter) that then provides a target for the dialysis technician to insert the two needles that are required to place a patient on the dialysis machine. Some advantages of a native AV fistula may include, for example, longevity, immunity from infection, and low cost. This type of fistula has the longest life span of all known types of vascular access, lasting from several years up to twenty years or more, with the possibility of performing a secondary surgical intervention to salvage the functioning of the fistula even if complications do develop with the fistula over time. Also, since the fistula is constructed of native tissue, it is relatively immune to infection. Moreover, the fistula is cheaper to construct since there is no requirement for a costly catheter or synthetic graft.
On the other hand, since there are limited sites for the creation of a functioning fistula in each patient, the current standard of care is to perform the fistula in the most distal vessels in a patient's upper extremity where a preoperative assessment indicates that the fistula has a reasonable chance for maturing successfully. A 20% failure rate is considered acceptable for first time fistulas as vascular access surgeons try to maximize the available sites in a patient, cognizant that patients may require new fistulas at other sites in the future if the primary fistula eventually fails. This 20% failure rate can lead to further operations and, thus, significant additional costs and inconvenience to the patient.
Synthetic Graft Fistula. A third mode of vascular access requires the placement of a synthetic graft in a subcutaneous position, usually in a patient's upper extremity. The technician achieves access to the vascular system by placing needles directly into the easily palpable graft. Some advantages may include that the graft provides a reliable, easily accessible conduit to access to connect a patient to the dialysis machine. This choice of access is particularly valuable in patients who do not have the requisite minimally sized vein that will permit the establishment of a native AV fistula.
On the other hand, the cost of such a graft is approximately $3,292 (US) per patient. Also, the most commonly placed grafts require several days and up to several weeks for perioperative swelling to decrease and for the grafts to become sufficiently incorporated into a patient's tissues to allow safe access via the graft. The graft can also become infected by inadvertent lapses of sterile technique by the dialysis technician or through seeding from distant sources in the patient. An infected graft frequently requires a very costly and inconvenient (to the patient) series of procedures that includes removal of the infected graft, placement of an interim dialysis catheter, and a subsequent implantation of a new graft after the infection has been definitively treated to reestablish vascular access. A synthetic graft can also be prone to development of early or late thrombosis due to its synthetic, foreign quality.
Moreover, the site of the venous anastomosis between the graft and the patient's native vein can be a frequent site of stenosis that develops from a mismatch in the distensibility characteristics of the patient's native vein and the synthetic graft. This can require secondary costly surgical or endovascular interventions to correct the problem and to preserve continued functioning of the graft as a viable access conduit. Some grafts may even form a stenosis within the graft due to a proliferation of fibrin and scar tissue that requires a secondary procedure to maintain the viability of the graft. Additionally, repeated puncture of a graft in the same location by the dialysis technician can lead to a pseudoaneurysm formation (i.e., a localized collection of blood) that can eventually lead to failure of the graft if not corrected. Improper technique by the dialysis technician can also result in a hematoma formation during access to the graft or following removal of the needles at the end of the dialysis run. The hematoma may make access to the graft in that location difficult or impossible for a period of time, and may lead to occlusion of the graft.
Methods of vascular access that require fistula access are highly dependent on the skill of the dialysis technician. A fistula that, at maturation, is somewhat smaller than desirable, or is located deeper in the patient's tissues thereby presenting a less easily palpable target than normal, is more likely to be damaged during attempts to access the fistula. In the United States, the preferred method that is taught to access native fistulas is the step ladder approach, i.e., constantly moving the locations where the two access needles are placed in the fistula. The protocol of sticking needles into the fistula at different locations at each dialysis session leads to increased pain experienced by the patient since the effect of a localized area of insensitive scar tissue—e.g., where the fistula is accessed using the buttonhole technique (discussed further below)—is never allowed to form. Moreover, the native fistula may require at least 6 weeks and sometimes up to several months to mature, i.e., to grow to an adequate size and increased thickness of its walls that will allow the vessel to be safely punctured with a needle. During the maturation time for a fistula, a bridging dialysis catheter must be placed in the patient's central venous system to allow a patient to be dialyzed. Thus, there exists a need for a vascular access device that is capable of being used prior to fistula maturation.
Another approach, the buttonhole technique to access fistulas, has been shown in some studies to increase the longevity of a fistula while decreasing complications associated with moving access sites to different locations in the fistula during subsequent dialysis sessions. Some advantages of the buttonhole technique may include: (a) two nearby needle puncture points to access the fistula (approximately 3 cm apart) require only a relatively short functioning and accessible fistula to access the bloodstream; (b) blunt needle access through a fistulous opening in the skin into a scar tissue cylindrical track that leads the needle down to and into the vessel causes less patient discomfort (c) the narrow cicatricial cylindrical tract self-seals relatively easily with thrombus after removal of the needles following a dialysis run, eliminating the incidence of perifistula hematomas on the front wall of the fistula that can temporarily, or even permanently, incapacitate a fistula; and (d) after a cicatricial track has been established, blunt needles can be used to access the graft, decreasing the incidence of needle point damage to the back wall of the fistula when inserting needles.
A disadvantage of the buttonhole approach is that it requires a highly skilled dialysis technician to create a button-hole track. Ideally, a single, highly-skilled technician will repetitively perform the needle insertion on the same patient during the initial dialysis sessions, following the exact needle track in the same patient (same entrance point, same angle, same depth) every time for the first 10-15 access events until a well formed tract has developed. The logistical difficulty of having the same highly-skilled technician available for the first 10-15 access events in an individual patient currently limits the wider applicability of this technique.
U.S. Pat. No. 8,414,530, to Roger Alan Mason, herein incorporated by reference in its entirety, teaches the use of a vertically oriented chamber which guides a needle to a site in a blood vessel. Improvements to this device have been made which are incorporated into the present disclosure.
Vascular access devices that substantially overcome the foregoing disadvantages are needed.